Ultrasound offers a unique approach to image-guided therapy. First, tumor vasculature is detected using echo contrast imaging. Next, focused, higher-intensity ultrasound pulse sequence is applied to activate contrast/drug carrier material and release the therapeutic agent in the insonated area. In this application we propose the design and evaluation of a new generation of ultrasound-triggered drug carrier materials. Drug carrier microbubbles and liposome constructs will be applied to release antitumor agents or thrombus-generating enzyme into tumor vasculature. Selective drug deposition in the tumor mass will be achieved. Targeted cytotoxic effect on the tumor and targeted thrombosis will result in restriction of tumor growth and apoptosis. Specific aims (R21 Phase): 1. Prepare targetable microbubble drug delivery constructs and perform ultrasound-mediated release of model dye markers from liposomes, liposomes attached to microbubbles, and microbubble carriers. Evaluate release efficacy as a function of liposome/particle membrane composition, structure, phase transition temperature and ultrasound intensity, frequency and pulse characteristics to achieve optimal release. 2. Evaluate targetability of microbubble/liposome/drug constructs to activated endothelium in cell culture, assess drug release, gel and endothelial cell culture deposition. 3. Study ultrasound-mediated "triggering" activation of microbubble/liposome/enzyme constructs in vitro;evaluate release and therapeutic enzyme availability to convert the substrate. 4. Assess the ability of ultrasound energy to destroy microbubble drug carrier systems in an in vivo subcutaneous tumor on demand with image-guided targeting of ultrasound application focus. Specific aims (R33 Phase): 1. Study acute toxicity, biodistribution, vascular behavior and targeting of microbubbles and microbubble-liposomes constructs in a mouse model after intravenous administration comparing echo imaging, fluorescence and radioactive labeling of shells and contents of drug carrier particles. 2. Investigate in vivo accumulation of microbubbles, liposomes/complexes, and encapsulated cytotoxic agents in the areas of insonation, by ultrasound imaging, biodistribution of radiolabeled and fluorescent markers, fluorescence in vivo optical imaging, and tissue histology, as well as longer-term survival animals studies. 3. Perform ultrasound activation of thrombin drug carrier constructs;release thrombin selectively in the areas of model vasculature during intravital microscopy. Monitor blood and microbubble flow through target tissue. 4. Demonstrate arrest of tumor growth by ultrasound-triggered release of thrombin from microbubble constructs selectively in the areas of tumor vasculature during insonation of a solid tumor, per se and in combination with cytotoxic drug-loaded particles. Monitor blood flow within the tumor after treatment. Perform final optimization of the drug carrier formulation and ultrasound activation parameters.